- Create 003_quick_add_library.sql with quick_add_items table and user index
- Add QuickAddItem struct to models.go following Category pattern
- Add ListQuickAddItems, CreateQuickAddItem, UpdateQuickAddItem, DeleteQuickAddItem to queries.go
- Create 002_templates.sql: item_tier enum, ALTER budget_items, templates and template_items tables with CHECK constraint
- Add ItemTier type with fixed/variable/one_off constants to models.go
- Add ItemTier field to BudgetItem struct
- Add Template, TemplateItem, TemplateDetail structs
